Telephone trunking system



April 29, 1930. N. H. sAUNDERs 1,755,214

TELEPHONE TRUNKING SYSTEM Filed Aprill 28, 1928 2 Sheets-Sheet l .l A 195ml? w RN S \n Inuen nr :Nar-man H. Saunders N. H. sAUNDERs 1,756,214

TELEPHONE TRUNKING SYSTEM Filed Aprii 28, 1928 2 sheets-sheet 2 April 29, 1930.

f tem in which thenormal Patented Apr. 2,9, 1930 unirse sra NORMAN H. sAUNDERs, or noi'rnwoon,v rnnnors, AssreNon To COMPANY, or xANsAs crrY, Mrssoirni,

` ineen A coaroriAricn er DELAWARE mnnnrnenn TnUNxiNG sxsrniir Application tied Aprn as,

terferences are greatly reduced if all ground andfbattery connections are disconnected fromthe interofce trunk conductors during the period of conversation. In the application of Clarence E. Lomax, Serial No, 184,197,

tiled April 16, v1927, atrunking arrangement for two-way trunks between two automatic exchanges is shown in which lthe normal batteryand ground connections are disconnected y froinlthe trunk duringthe periodof conversation. 4' y rThis invention mayk bey considered an improvement and further development of the arrangementshownin the above reference,` its Y object being the provision oi a trunking sysground and battery connections are disconnected from the interoffice trunk line during they period o conversation when the call is extended from a inanualto an automatic ,exchange or from an automatic to a manual exchange, and further, the provision of a trunking system iny which when a call is extendedromone Vexchange to another exchangeby way/oan intermediate excliangethe normal groundfand" battery connections are disconnected from the trunk between the iirst exchange and the intermediate exchange as well as from the trunk between he intermediate exchange and the second exchange during the period oi. conversa-tion.` ln telephone pai-lance a trunk tree from all battery and ground connections is known as a dry trunk, andthe operation off disconnecting the ynormal battery andl ground connections from the trunk is known j as cutting the trunk dry.

This invention and its various features will be described indetail-in the following specification with the aid ofV the accompanying drawings comprising Figsl andl 2. These drawings, vwlienlFig. lis placed tothe lett,-

192s. serial No. 273,512.

ofFig. 2 show by mea-ns ofthe usualschematic circuit diagrams a preferred embodiment of the invention. j f

yThe system chosen to illustrate this invention comprises three exchanges, two manual exchanges and an automatic exchange with interoce trunks between the automatic ex-V change and each manual exchange, although theinvention is in no way limited to any particular size system'. The apparatus shown to the left of the dotted vertical line in Fig.

l is located in the lirst manual exchange,

which will be'refei'ied to as exchange A. The

apparatus shown to the right of thedotted verticarline in Fig. 1 and to the left of the dotted vertical line in Fig.l 2 islocated in the automatic exchange, which will be referred to as exchange VB; andthe apparatus indicated to the right oic the dotted vertical line in Fig.

2 is locatedin the second manual exchange,

whichwill be referred to as exchange C. The trunk comprising conductors 8l and 82 vis one of the trunks extending from the exchangeA to'exchangeB.` This trunk. is ac cesible at exchange A at jack J, and terminates A.exchange B in the selector S by way of the outgoing repeater` OR. and the incomjing repeater Ht. ,The trunk comprising conductors 281 and 282 is one of tlie trunks ex. tending vfrom exchange C tovr exchange B.

This trunk is accessible at exchange C at jack J2, andA terminates at exchange vl in the selector S by way of the outgoing repeater OR and the incoming repeater 1R. A trunk relay group,lsuch as relay group 'FRG is associated with the manual end of each interofiice trunk.,v rlhe trunk relay group TRG,

the incoming repeater IR', and the outgoing repeater OR, indicated onlyk by rectangles, are similar to the trunk realy group TRG, the

Vincoming repeater llt, and the outgoing repeater OR, respectively.y

The local automatic switch train in exchange B is diagrammatically shown at the bot-toni of Fig. 2, comprising the individual lineswitch LS, the local selector S2, and the connector C. The selectors, such as selector S, have access in their banks to the trunks toexcliange C by way of the outgoing repeaters, such as repeater 0R, and also have Tes raraar erst-ea nnsnnvn 'HOLDING' access to the connectors in exchange B. rl`he selectors, such as selectors S, have access to the trunks to exchange A by Way of the outgoing repeaters, such as repeater OR', and also have access to the connectors of exchange B. The local selectors, such as selector S2, in addition to having access to the connectors in exchange B, also have access to the trunks to exchange A and to the trunks to exchange lo 1B by Way of the outgoing repeaters.

In the description it is assumed that the selectors and'connectors in exchange are of the Strovvger vertical and rotar Y type, and that the cords used by the operators in the manual exchanges arel of the type which have battery and ground normally connected to the tip and ring conductors, respectively, and which impulse over the tip conductor and maintain ground connected to the ring conductor. during the impulsing period. The cord circuit O, shown in Fig. 1 is a skeleton of a cord of this type. Another similar cord circuit is indicated 'in Fig. 2 at O.

A further understanding of the invention is obtainable most easily by following through the operations performed in the establishment of various connections. For this purpose it Will be assumed that the operator at exchange Alias receivedL a call for a subscriber. at exchange C. lt will be assumed that she has 'answered the incoming call bv means of the cord circuit O. To further extend the connection, the operator inserts the calling` plug P of thecord circuit O into the jack of an idle trunk extending to exchange B, the jack J for example. inserting `)luoP into 'ack J closes a circuit for rela l b 5 in series With sleeve relay 60 over the sleeve conductor of plug Pand jack J. Relay 5 operates and closes a circuit for relay and lamp L at contacts 6. Relay 20 operates and bridges the calling device across the tip and ring conductors of plug P at contacts 21 and 23. Relay 60, in operating over the above circuit, closes points in the talking circuit at contacts 62 and 65 and closes a circuit for relay at contacts 64 which includes contacts 43, ring oi1 jack J and plug P, contacts 23, and o-normalcontacts 16 of the calling device D. Relay 40 operates and closes a holding circuitfor itself at contacts 42, disconnecting itself from the ring conductor by separating Contact 43, and closes the circuits forrelays 55 and 75 at contacts A1. Relay 75 operates and by separating contacts 76 and 79 disconnects relay 70 from the trunk conductors and by closing contacts 77 and 78 further prepares the talking circuit. Relay 55 operates and by closing contacts 56 closes the bridge across the trunk conductors 81 and 82, thereby closing a circuit for relay in series With the line relay 130 of the incoming repeater IR at exchange B.

Relay 130 operates and closes the circuit of relay 135 at contacts 132, and closes theV of the calling'device D.

bridge across conductors 141 and 142 at contacts 181. As a result, the line and the release relays in the selector S operate to prepare the selector S for operation. Relay 135 of the repeater llin operating, prepares the circuit o relay 105 at contacts'l, and grounds the release conductor 2,02 at contacts 137 at the same time also completing the circuit for the polarizing Winding oit' relay 100. `The presence or' ground potential on conductor 202 marks'this trunk busy.

After inserting plug P into jack J, the operator at exchange A dials the number assigned to exchange C. When the calling device l) is moved oil-normal, contacts 16 are opened and contacts 18 are closed, thereby placing ground potential on the ring conductor. This causes the operation of relay 30, battery potential being connected to the upper terminal of its Winding bywvay of contacts 36 and 4,2'. Relay 30, in operating, connects theimpulsing relay to the tip conductor at contacts 31, relay 55 thereafter being energized from ground at the impulsing springs TWhen the calling device is released, the circuit of relay 55 is opened a number of times corresponding to the digits for which thecalling device Was positioned. Relay 55 deenergizes and reenergizes a corresponding number of times, opening the circuit of line relay 130 at the eX- change Bat contacts `56 at each deenergization. Line relay 130 repeats the impulses to selector S at contacts 131. The selector S then operates in the usual manner, raising its Wipers opposite the level corresponding to the digit dialed and then selecting an idle trunk in that level. During the impulsing period, slow-to-release relay 105 is maintained operated, its circuit being closed each time that relay 130 deenergizes. Relay 105, in operating, short-circuits the left hand windings of repeating coil R at contacts 106 and 107, and short-circuits the entire right hand side of this repeating coil at contacts 10S, the purpose being to improve the impulsing circuit.

lt Will be assumed that the trunk selected is the one comprising conductors 201, 202, and 203,`Which extends to exchange C by Way of the outgoing repeater OR. lfhen this trunk is seized, line relay 220 of the repeater OR closes the circuit of relay 230. Relay 230 operates and places ground on the release conductor 202 at contacts 281 to hold the selector S operated. At contacts 232 the circuit of the cut-off relay 240 is Closed. Relay 240, in operating disconnects the repeater IB. from the trunk conductors 281 and 282 and completes the signalling circuit by closing contactsy 242 and 243. .Ringing current trom the generator G is nowv supplied to the trunk conductors and causes the operation of the relay in the trunk relay group THG corresponding to relay or the trunk relay group TRG. This relay operates and closes and ringconductors of plug P. andicloses av lock-ing circuit for itself at1 contacts` coriespending to contacts 17 2, and cl-osesla circuit fornlarnpL2 Vatcontacts vcorresponding to contacts 71. j ,v .After dialling the digit, the operator at exchange A presses key K. This operation closesthe circuit of thev lower winding of ref laylO. Relay 10 then operates and disconnects relay 5 from :the sleeve of plug P and vcloses a holding circuit for itself yto the sleeveof-` P by closing VContact 11, opens the circuit of relay 20 by separating contact 14 and. closes a new circuit for lainpvL at contacts. 13. Relay 20 then deenergize's andV disconnectstlie callingy device D from the tip points in the'talkingconnectionby closing contacts 22 and 24. -B-elay 2'is bridged across the conductors of the cord, but since relay 50 is operated, holding the ybridge across the tip "andring ojackJ open at vcontacts 51, relay 2 remains` deenergized and the lainp L re' niainslighted.Y j f l.

Upon noting the lighted condition of laingpfL2, the operator at exchange C answers lthe ycallby inserting the answering plug or n an idle cord such as the plug l?8 (which corresponds tov plug P- oi" cord circuit O) into jack J?. They sleeve relay corresponding to relay thenlenergizcs overA the sleeve concorresponding to contacts 64, and closes points in the talking circuitbyclosing contacts corresponding to contacts G2 and 65. The relay corresponding to relay 40, in operating, closes tbecircuit of the relayslcorresponding to revlays and 55. at contacts corresponding to contacts 41. These relays upon Ioperating across the'trunk conductors 281 and 282. The closing of the bridge across the trunk conductors closes a directcurrent` circuit for the lower winding of ring-cut-oii1 relay 210 l at exchange B.` Relay 210 thereupon operates, closing a locking circuit for itself at contacts `213, opening the ringing circuit and disconnecting battery, and Vground from the trunk conductors by separating contacts 211 and 219, and closing points in, the talking "circuit *at contactsy k212 and 218.A Furthermore, by separating contacts 215 and 217 and closingv contacts 21l1vand 216, relay 210 reverses the current over, the Conductors 141 fand142 and through the uppery winding of Aupolarized relay 100. Relay 'not having ,trunk conductors extending.` to exchange Al responded previously, now operates and by separating contacts 102 opensv the circuit of relay 135 and by closing contacts 101 closes the circuit of relay .120. Relay 120 operates,

disconnecting the line relay 130 from the by separating contacts 122 and 125 andbridging relay across the trunk conductors byl Closing/Contada. 12.3 and .1.24, At Contacts ductorand causesthe operation of the relayy vcorrespondingto relay L10 by closing contacts complete the talking circuit, closi'ng a bridge Y rent bridge across the tip and ring of jack J', i

contact 51, thereby closing andienergizing circuit for relay2 of the cord circuit 0. Relay 2, in operating,eopens the circuit; of

lamp L at contacts ,3, thereby extinguishing" thel lamp.y The extinguishment of lamp L at this time signals the operator at exchange g, A tliatfthe call has been answered. To con-.1

Verse withl the operator at exchange B the operator at exchange A merely operates-her listening key K to connectlier telephone set' to the 'talking connection.

It should be particularlyl noted thatboth i the trunk from exchange A to exchange B and also the trunk from exchange B to exchange C have been cut dry, this li'avin'g taken i place responsive to the call being answered at exchange B. Tha-t is, when the operatorat exchange B answered the call the ring-cuteoff relay 210at exchange B Vdisconnected the exchange battery normally bridged) Vacross the conductors 281 and 282 from the trunk conductors and reversed the current over the conductors 1411 and 1412 which caused y the operation of the polarized relay 1D0 in the repeater IB, which in turn caused-the disconnection of the exchange battery and line relay 130 from the trunk conductors 81 and 7 8,2v extending to exchange A. i l Y The operator at exchange C then completes the connection to the desired subscriber in the usual manner.

At the termination of the conversation between the two subscribers, andv afterthe operators have received the V usual disconnect n signals, both operators will reinove the plugs of their cords from the jacks of the trunks, usedin the connection. Vfhenthe plug l is removed from jack J,.the `circuit of relay 60 is opened. Relay 60 deenergizes; and opens the circuit of relay 4:0. Relay 40 is slow to release and therefore maintains the circuit of relay 75 closed an interval after its own,-

circuit is opened. During thetinie that relay 7 5 is maintained operated after relay 6Gv has restored, battery andv ground rare con-V nected to trunk conductors 81 and 82y by way of contacts 61 and 66. This causes the 'opere ation of relay 110 bridged acrosstlie trunk conductors during the. period ofconversation at the exchange B. Relay 110, in energizing. opens the circuit of relay l120 at contacts 113 and ,bridges litself across the, conductors 81 andl 82,*independent of the contacts of,V relay 120 at contacts 111 and 114, and also connects ground to release conductor 202 at contacts 116. Relay 120, in restoring, opens the bridge across conductors 141 and 1112 thereby opening the circuit ofrelay 220 of the outgoingl Vrepeater OR. Relay 220 deenergizes and y.2110 by separating contacts 232.

As soon as relay 7 5 at exchange A restores, ground and battery are again disconnected from the trunk conductors 81 and 82, and the circuit of relay 110 of repeater IR at exchange B is opened. Relay 110, in deenergizing, again connects the line relay 130 across the trunk conductors 81 and 82 Vand removes ground potential from the release conductor 202 at the same time opening the circuit of the polarizing winding of relay 100 at contacts 116. Both trunks are thus placed in their normal condition. The purpose of causing relay 110 when'operated to bridge itself across the trunk conductors 81 and 82 is primarily to maintain ground on the release conductor 20 to vkeep this trunk marked busy until after relay 7 5 at exchange A has restored.

Connections may be established from exchange C to exchange A over these'same two trunk lines, and the operations performed will be the same as'those described above. Such a connection, however, would extend by way of the incoming repeater IR', selector S', and the outgoing repeater OR.

In this system, the subscribers in the automatic exchange B may also extend connections to either the manual exchange A or the.

manual exchange B, since the banks of the selectors such as selector S and the selectors such as selector S are multiplied with the banks of the local selectors. To extend a connection to the exchange C, for example, a subscriber at exchange B merely removes his receiver and dials the digit assigned to the exchange to which he wishes to extend a connection. A selector such as selector S2 operates and raises its wipers to the level corresponding to the digit dialled and then selects a trunk to the exchange C. The outgoing repeater of the trunk selected operates in the same manner as when selected by a selector such as the selector S. The reversal of current when the ring cut-off relay operates responsive to the answering of the call has no effect other than to cause the calling subscribers meter to operate if he is a measured service subscriber.

Connections may also be completed from either manual exchange to a subscriber at the automatic exchange. To extend a connection to a subscriberv at exchange B, the operator at exchange A follows the same procedure as she did in extending a connection to exchange C, except that she dials the com- Y to an idle connector of the proper group; and Y the connector operates responsive to the last two digits' to extend the connection to the called subscribers line .and signal the called subscriber. Y wWhen the called subscriber anwers, thel connector reverses the current over the trunk to the selector, which causes polarized relay 100 in the repeater IR to operate with the results previously described.

rI'his completes the description of this invention. I/Vhat is considered new and is desired to have protected by Letters Patent is specicaily stated in the appended claims.

What is claimed is:

1. In a telephone system, a trunk line extending from a first to a second exchange, a

second trunk line extending from the second exchange to a third exchange,an automatic switch at the secondexchange terminating said iirst trunk line, means for operating said switch toY connectV with said second trunkY line to extend a call fromV the first exchange to the third exchange, abatteryat said second exchange connected to both said trunk lines, and means responsive to the answering of the call .for disconnecting said battery from both of said trunk lines.

2. In a telephone system, a trunk line ex#V rom both of said trunk lines, a signal control relay at the first exchange, and means responsive to the disconnection of said battery from the first trunk for actuating said signal control relay. Y Y

3. In a telephone system, a trunk line extending from a first to a second exchange, a second trunk line extending from the second exchange to a third exchange, an automatic switch at the second exchange terminating said first trunk line, means for operating said switch to connect withV said second trunk line to extend a call from the first to the third exchange, a battery at the second exchange, a line relay normally connected to the iirst trunk line in series with said battery for controlling the operation of said switch, means for signalling over said second trunk line, a cut-off relay and means for connecting it to the second trunk line in series with'said bat- I' of both .trunk lines.l f

tery when a call is extended from said second trunk line, said cut-ofi yrelay being responsive to the answering of the call for interrupting the signalling and for disconnecting said battery from said second trunk line, and means responsive to the operation of fsaid cut-oit relay for disconnecting said batteryfrom said first trunk line.

said repeater to said switch, a secondtrunk line extending from the second exchange to aA third exchange, means `for operating said switch to connect vwith said secondtrunlline to extend a callfrom the first to the third ex? change. a battery at the secondexchange, means forestablishing a-fiow of currentrover said conductors,'a line relay normally con` nectedto the first trunk line in serieswit-h said battery for controlling the operation of said switch,vmeans for signalling over` said second trunk line, a cut-off Vrelayand means for connecting itto the second trunk line in series with said battery .when a call is extended over the secondtrunk line, said cut-ofi relay being responsiveto the answering of the call for interrupting the signalling, for disconnecting saidbattery from' said second trunk iine,'and for reversing the flow fot current in said conductors, yand means responsive to saidreversalof current for dis'- connecting said battery and ysaid line relay from said first trunk lline. Y y Y v 5. In a telephone system, two serially related trunk lines for extending a'call, abattery normally bridged across the conductors of each of the `trunk lines, and meansv responsive to the answeringof the call for disconnecting said battery from the conductors 6: In a telephone system, means including two serially related trunk lines for extending ,a call, the yfirst trunkline comprising two inductively connected sections, meansiresponsive to the initiationof the call for pro-- Aducing a flow of current inthe two sections Vof the yfirst trunk line, and responsivejto the answering ofthe call for producing a flow of current 'in the second trunk line, means responsive to the flow of current in the 'second trunk line Jfor reversing thecurrent in the second section of the iirstftrunk line,

and'ineansresponsive to the reversal of cur-l 'rent in the second section of the first trunk line foriiiterrupting the How of the current in` the first section of the first trunl line.

'TQIn va telephone system, a trunlr'line terininating in an automatic switch, a second trunk line, a battery connected to both trunk lines, means `controlled by successively interrupting a flow of current from-said bat ,Y tery over said nrst trunk line for operating ,rent over either trunk line.

said switch to connect with said second trunk line to extend a call, means responsive .to the answering of the call for disconnecting said battery from both said trunk lines, and' means for maintaining said Vswitch operated '70 independent cf the existenceV of aflow of cur- 8. VIn a telephone system, a trunk ,line extending froin a first to a second exchange, a second trunlrline extending from the `second exchange to thirdy exchange, an automatic switch at the second ei-:change terminating said first trunk iiiie, means for operating` said switch to connect with said second trunk line to Vextend a cail from the iirst tothe third v50 exchange, a battery at the second exchange,

a line relay normally connected to' the first trunk line in series with said battery for controlling the` operation of said* switch, means for signalling over said second trim'kjrgg line, a cut-oft relay and means for connectingl it to thel second trunk line in series with said battery/when a call is extended over lsaid second 'trunk line, said cut-off relay beingA responsive to the answering of the call for, 9@ interrupting the signalling' and for Vdiscon-'l'Y f necting said battery from said second trunk line, means responsive [to the'operation of saidcutLoii" relay for disconnecting said battery from said first trunk line, a second battery at the rst exchange and means for f vmomentarily connecting it to said first trunk l l causing the release offsad switch.

'9. In a telephone system` a trunk lineterlminating in an automatic switch, a second trunk line, a battery connected to both trunk lines, means controlled Lby successivelyy in- 105 terrupting a flow of -current from said first :trunk 'line for operating said switch to connect with'said second trunk line to extend a call, means responsive to the answering of 'the call for disconnecting said battery fromwllo both said trunk lines, means for'maintaining f said switch operated independent ofthe lex- Vistence of aflow' of'current over either trunk line, a second battery, means for momentarily connecting it Vto said trunllvline at^v the terminationfof vthe Vcall, Vand means re`' sponsive to the connection of said secondbattery to saidv trunir'line for releasingisaid Y switch.-

lO. In a telephone system, two serially vre- .120 lated trunk lines for extending call7 a batf: i tery normally bridged across the conductors of each of the trunk lines, means responsive to the answering of the call for disconnecting said battery Vfrom the conductors of *both K trunl'lines', a vsecondi battery, means formtv V-mentarily,vconnecting said second battery to the first trunlr line, and means -responsiveto theniomentary connection of said second battery .to the first trunk linenfor disabling said 139 iirst means to cause said first battery to be again bridged across bothk trunk lines.

11. In a telephone system, means includ- .ing two lserially related trunk lines for extending a call, the iirst trunk line comprising two inductively connected sections, means responsive to the initiation ot1 the call for Vproducing a iiow oi current in the two sections of the first trunk line, and responsiv to the answering of the call for producing a ow of current in the second trunk line, means responsive to the flow of current in the second trunk line for reversing the cnrrent in the second section of the iirst trunk line, means responsive to the reversal of current in the second section of the first trunk linerfor interrupting the dow of current in the iirst section of the first trunk line, meansV responsive to the termination oi the callfor again producing a i'iow of current in the iirst Vsection of the first trunk line, and means responsive to the second iiow of current in the first section of the first trunk line for interrupting the flow of current in the second sectionv of the first trunk line.

12. In a telephone system, two serially related trunk lines for extending a call, a battery normally bridged across tlie'conductors of both trunk lines, means responsive to the answering of the call for disconnecting said .battery from the conductors of each trunk y, line, a second battery, means for momentarily connecting said second battery to the iirst trunk line, a relay responsive to the connection of said second battery to the rst trunk line, means responsive to the energization of said relay for causing said first battery to be again bridged across the second trunk line, and means responsive to the deenergization of said relay for causing the irst battery tov be again bridged across the iirst trunk line.

` means responsive to the deenergization ot said relay for causing said line relay and said battery-to be again bridged across the conductors ofsaid trunk line.

14; vIn a telephone system, atrunk line and means for seizing it to extend a connection.

a battery connected to said trunk line to iurv nish current for controlling the establishment of the connection, means for marking 'said trunk busy when it is seized, means responsive to the answering or the call for disconnecting said battery from saidtrunk line,

means for producing Va momentary iow oi current over said trunk line, a relay responsive to said momentary flow of current for effecting the reconnection of said battery to lsaid trunk line, and vcontacts on said relay y conductor and contacts on said self-locking relay orsaid third relay, an impulsing relay, and means controlled'by said third relay for connecting said impulsing relay to the other talking conductor of said trunk line to place itunder the control of said calling device. f Y c 16. In a Vtelephone system, a trunk line, a cord circuit and means for connecting it to said trunk line, a self-locking relay, a sleeve relay responsive to the connection of said s cord circuit to Asaid trunk forclosing an initial energizing circuit including one talking `conductor of said 4trunk line for said selfvlockingrelay, a third relay, a calling device` iii the cord'circuit, means responsive to the movement of said calling device oit normal for closing a circuit including said talking conductor and contacts on said self-locking relay for said third relay, an impulsing relay, means controlled by said third relay for connecting said impulsing relay to the other talking conductor of said trunk line to place it under the control of lsaid calling device, a battery, and means controlled jointly by said sleeve relay and said self-locking relay `for momentarily connecting said battery to said trunk line. Y

17. In a telephone system, a trunk line connecting a first and a second exchange, a

second trunk line connecting the second eX- change to a third exchange, means including said trunk lines for extending a call from the iirst exchangeto the third exchange, a battery connectedV to said trunk lines, and means Yresponsive to the answering of the call for disconnecting said battery from both of said trunk lines.

Viirst to the third exchange, Val battery connected to said trunk lines, means responsive to the answering of the call for disconnecting said trunk line, a relay responsive to said resaid battery .from both of saidtrunlr lines,

and means responsive to the termination of thecall for again connecting` said battery to said trunk lines.

19. In a telephone system, a trunk line connecting a first and a second exchange, a second trunk lline connecting the second eX- change to a third exchange, means including said trunk lines for extending a call from said first to said third exchange, a battery connected to said trunk lines, means for signalling said third exchange, a cut-off relay in said second exchange responsive to the answering of the call, and means controlled by said cut-off relay for disabling said signalling means and for disconnecting saidv battery, from said trunk lines.l v

2O.` -In a telephone system, a trunlr line comf prising'two indnctively connected sections used to extend a call, a battery normally bridged across each offsaid sections, means lresponsive to the answering of the call for reversing the battery in the second section of said trunk line, and means responsive to the reversal of battery in the second section of said trunk line for disconnecting' said battery from the first section of said trunk line.

21. In a telephone system, a trunl; lineV comprising two inductively connected sections'used to Xtend a call, a battery normally bridged across each of said sections, means responsive to the answering of the call for reversing the battery in the second section of said trunk line, means responsive to thereversal of battery in the second section of said trunk line for disconnecting said battery from the first section ofA said trunllrline, and means responsive to the termination of the call for again connecting said battery to the two sections of said trunk line.

22. In a telephone system, a trunk` line comprising two inductively connected sectionsused to extend a. call, a battery normally connected to each of said sections, means responsive to the answering of the call lfor reversing the battery in the second section of versal of battery, asecond relay, means re` sponsive to the energization of said first relay for disconnecting said battery from the first section of said trunk line and for ybridging said second relay across the conductors thereof, means forfmomentarily energizing said second relay at the termination of the call, and' means responsive to the operation o f said second relay for again connecting said battery to the first section of said trunk line.

24.V In a telephone system, a trunk line comprising two inductively connected sections and terminating in an automatic switch, means including said trunk linevand said switch for extending a call, a battery normally connected to each of the sections of said trunk line, means responsive to the answering of the call for reversing the battery inthe second section of said trunk line, a relay responsive to said reversal of battery, a second relay, means responsive to the energization of said first relay for disconnecting said batttery from the first section of said trunk line and j for bridgingfsaid second relay across the con-l ductors thereof, a vsecond battery, means responsive to the termination of the call for momentarily connecting said second battery to the first section of said trunk line to` operate said second relay, means responsive to the .energization of said second'relay for releasing said switch, and vmeans responsive to the deenergization of said second relay for again connecting said first battery to the two sections of said trunk line. Y

25. In a telephone system, a trunkline, a cordy circuit and means for connecting it to said trunk line, a calling device in said cord (circuit, an impulsingrelay, means responsive Vto the connection of said cord to said trunlr line and the movement of saidcalling device off normal for completinga diallingl circuit including said calling device, one talking conductor of said trunk line and said impulsing relay, a battery, and means responsive to the disconnection of ysaid cord yfromy said trunk line for momentarily bridging said battery across the conductors of said trunk line.

y In witness whereof, I hereuntosubscribe my name this 25th day of April, A. D. 1928. NORMAN H. SAUNDERS.

son

'iso 

